Problems extruding a circle along circular path
gandalf3's answer is the most likely answer and solution to the problem. Another thing you could try is shrinking the bevelled object with AltS. However, I see no advantages in obtaining a torus from curves that way. Why not just add a Curve > Circle and tweak the settings. To fatten, increase the depth and to get it smoother/rounder, increase the resoulution. Much easier to tweak and less work.